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United States Patent |
5,056,488
|
Eckert
|
October 15, 1991
|
Fuel injection system in particular unit fuel injector, for internal
combustion engines
Abstract
A fuel injection system for internal combustion engines, having a pump
chamber defined by the pump piston and a pressure chamber adapted to
communicate with the injection nozzle; and further including an
intermediate piston disposed between the two work chambers, in which
during the compression stroke of the intermediate piston a throttle
conduit which branches off from the pump chamber can be opened, in order
to allow some of the fluid to flow out of the pump chamber while leaving
the injection quantity located in the pressure chamber unchanged, to
thereby attain a lengthening of the injection duration.
Inventors:
|
Eckert; Konrad (Stuttgart, DE)
|
Assignee:
|
Robert Bosch GmbH (Stuttgart, DE)
|
Appl. No.:
|
508431 |
Filed:
|
April 13, 1990 |
Foreign Application Priority Data
| Apr 21, 1989[DE] | 3913128 |
| Feb 15, 1990[DE] | 4004610 |
Current U.S. Class: |
123/446; 123/496; 239/88; 239/91 |
Intern'l Class: |
F02M 007/00 |
Field of Search: |
123/446,447,500,501,496
239/88-96,533.1-533.12
|
References Cited
U.S. Patent Documents
4235374 | Nov., 1980 | Walter et al. | 239/90.
|
4407253 | Oct., 1983 | Bauer | 123/506.
|
4489886 | Dec., 1984 | Kato | 239/88.
|
Foreign Patent Documents |
3700359 | Jul., 1988 | DE.
| |
Other References
"Bosch-Verteilereinspritzpumpe mit Fliehkraftregler", Bosch Technische
Berichte, Band 6, 1978, Heft 2, Bild 15 auf Seite 98 und Seite 99,
translation of AR: Bosch-Distributor Injection Pump with Centrifugal
Governor, Bosch Technical Instructions, vol. 6, 1978, No. 2, Fig. 15 on
pp. 98 and 99.
|
Primary Examiner: Miller; Curt Stuart
Attorney, Agent or Firm: Greigg; Edwin E., Greigg; Ronald E.
Claims
What is claimed and desired to be secured by Letters Patent of the United
States is:
1. A fuel injection system for internal combustion engines, comprising:
a fuel injector having a pump chamber provided with a reciprocable pump
piston;
a pressure chamber adapted to supply an injection nozzle of said injector
via a pressure line with a quantity of fuel to be injected;
an intermediate piston hydraulically dividing the pump chamber and the
pressure chamber of said injector;
a metering device associated with said injector delivering the quantity of
fuel to be injected to the pressure chamber during an intake stroke of the
pump piston;
means to define a supply onset of the injector by an injection fluid volume
present in the pump chamber, said volume being variable in controlled
fashion via a metering line;
and a throttle conduit (23) that branches off from the pump chamber (4),
said throttle conduit (23) containing a throttle (42) which is opened by
means of the intermediate piston (5) shortly before the end of a
compression stroke of the pump piston (1) but still during an effective
injection stroke of the intermediate piston (5).
2. A fuel injection system as defined by claim 1, in which the pump chamber
(4) is relieved toward a chamber of lower pressure by the intermediate
piston (5) toward the end of the compression stroke of the pump piston (1)
and in order to terminate the stroke of the intermediate piston (5).
3. A fuel injection system as defined by claim 1, in which the end of
supply is effected by the opening of a diversion conduit (22) of the
pressure chamber (6) to a chamber (16) of lower pressure, toward the end
of the compression stroke, by means of the intermediate piston (5).
4. A fuel injection system as defined by claim 2, in which the end of
supply is effected by the opening of a diversion conduit (22) of the
pressure chamber (6) to a chamber (16) of lower pressure, toward the end
of the compression stroke, by means of the intermediate piston (5).
5. A fuel injection system as defined by claim 1, in which the intermediate
piston further includes an annular groove (36) adapted to communicate with
the pump chamber (4), which groove cooperates with an opening, present in
a cylindrical bore (2) of the pump piston (1), of a relief conduit (21)
leading to the chamber of lower pressure, and that this opening is
preceded in the compression stroke direction by an opening of the throttle
conduit (23).
6. A fuel injection system as defined by claim 2, in which the intermediate
piston further includes an annular groove (36) adapted to communicate with
the pump chamber (4), which groove cooperates with an opening, present in
a cylindrical bore (2) of the pump piston (1), of a relief conduit (21)
leading to the chamber of lower pressure, and that this opening is
preceded in the compression stroke direction by an opening of the throttle
conduit (23).
7. A fuel injection system as defined by claim 4, in which the intermediate
piston further includes an annular groove (36) adapted to communicate with
the pump chamber (4),which groove cooperates with an opening, present in
the cylindrical bore (2) of the pump piston (1), of a relief conduit (21)
leading to the chamber of lower pressure, and that this opening is
preceded in the compression stroke direction by an opening of the throttle
conduit (23).
8. A fuel injection system as defined by claim 3, in which the intermediate
piston further includes an annular groove (36) adapted to communicate with
the pump chamber (4), which groove cooperates with an opening, present in
a cylindrical bore (2) of the pump piston (1), of a relief conduit (21)
leading to the chamber of lower pressure, and that this opening is
preceded in the compression stroke direction by an opening of the throttle
conduit (23).
9. A fuel injection system as defined by claim 5, in which the throttle
(42) of the throttle conduit (23) is provided in this conduit leading into
the cylindrical bore (2) of the pump chamber (4) and comprises a throttle
slit extending in the compression stroke direction.
10. A fuel injection system as defined by claim 6, in which the throttle
(42) of the throttle conduit (23) is provided in this conduit leading into
the cylindrical bore (2) of the pump chamber (4) and comprises a throttle
slit extending in the compression stroke direction.
11. A fuel injection system as defined by claim 7, in which the throttle
(42) of the throttle conduit (23) is provided in this conduit leading into
the cylindrical bore (2) of the pump chamber (4) and comprises a throttle
slit extending in the compression stroke direction.
12. A fuel injection system as defined by claim 8, in which the throttle
(42) of the throttle conduit (23) is provided in this conduit leading into
the cylindrical bore (2) of the pump chamber (4) and comprises a throttle
slit extending in the compression stroke direction.
Description
BACKGROUND OF THE INVENTION
The invention is directed to improvements in fuel injection systems, in
particular unit fuel injectors.
In a known Diesel injection system of this type (German Offenlegungsschrift
37 00 359), a high degree of freedom in terms of open and closed-loop
control interventions in the control processes pertaining to injection is
advantageously obtained by the use of an intermediate piston, specifically
by providing that quantities of fluid are metered largely independently of
one another in two separate chambers, namely the pump chamber and the
pressure chamber. One of these fluid quantities, located in the pump
chamber determines the supply onset, and hence, depending on the injection
quantity stored, the end of injection as well; the second fuel quantity,
metered into the pressure chamber, is injected as an unmodified injection
quantity. This advantage has a particularly favorable effect in direct
injection engines (in contrast to chamber engines), with the high
injection pressures they require, where the dictated high feed pressure in
the pump chamber and pressure chamber has a not inconsiderable influence
on the particular fuel volume, because of the compressibility of the fuel.
This change in volume would have a particularly disadvantageous effect
given the oblique-edge control means predominantly used in mechanically
controlled injection systems, where the quantity control is effected by
deviation during the compression stroke.
In the generic injection systems here, contrarily, although a fuel quantity
metered into the pressure chamber at low pressure via the metering device
is also compressed during the compression stroke, nevertheless it is
injected as desired, in the predetermined amount. The compressibility of
the fuel cannot have a disadvantageous effect. Since the speed of the pump
piston is rpm-dependent, that is, the piston speed is higher, the higher
the rpm, and whenever an adequate transmission pressure has been
established in the pump chamber as a result of the volume enclosed there,
this speed is transmitted directly upon the motion of the intermediate
piston; the result is a very short injection duration at high rpm and a
corresponding longer injection duration at lower rpm, at the same load or
in other words at the same injection quantity. In the short injection
duration available at high rpm, a maximum quantity (full load) must
necessarily be injectable, and at low rpm this is no problem because of
the longer period of time available. Through the various operating ranges,
with the injection quantity varying by a factor of from 1 to 30 from
idling up to full load, however, this condition means that the available
time during idling, which is relatively long because of the low rpm, is
not utilized for an optimal injection course, given the relatively small
injection quantities during idling. On the other hand, the engine noise is
particularly annoying during idling, although it is well-known that
lengthening the injection duration, which would theoretically be possible,
particularly in the idling range, would lead to a drop in engine noise.
In a known fuel injection system ("Bosch-Distributor Injection Pump with
Centrifugal Governor", Bosch Technical Instruction, Vol. 6, 1978, No. 2,
FIG. 15 on page 98 and 99; see also U.S. Pat. No. 4,407,253), some of the
fuel quantity pumped by the pump piston out of the pump work chamber flows
out via a throttle conduit during the compression stroke and during
idling, while another portion of the fuel attains injection. The injection
quantity required for maintaining idling is nevertheless injected, because
the mechanical governor of this injection pump compensates for the portion
flowing out via the throttle conduit by correspondingly shifting the
diversion of fuel from the pump work chamber occurring during the
compression stroke. With this division of the supply quantity, a longer
period of time is obtained for the portion to be injected than would be
the case if no fluid were to flow out via the throttle conduit.
Although theoretically it would be conceivable to provide such regulation
to lengthen the injection duration in the injection system of this generic
type, to do so would cancel out some of the originally obtained degree of
freedom. Furthermore, at very high injection pressures, the elasticity of
the fuel would engender additional control errors, which would be very
difficult to correct. This is true particularly for unit fuel injectors,
which have a very compact pumping region (pump chamber and pressure
chamber) and usually operate at very high pressures (up to 1800 bar).
OBJECT AND SUMMARY OF THE INVENTION
It is a principal object of the fuel injection system now to be discussed
and the primary advantage over the prior art that the fuel quantity in the
pressure chamber to be injected and metered at low pressure in the intake
stroke remains unchanged, even though in idling a corresponding
lengthening of the injection duration is attainable. The throttle in the
relief conduit has a predetermined constant cross section, so that in
combination with the piston speed and hence the effective supply duration
per cycle, an effective variation of the injection duration is possible,
which decreases with increasing rpm and conversely increases with
decreasing rpm, providing an optimal injection duration at a low idling
rpm. Depending on the injection quantity pumped during this injection
duration, a quantity of fluid flows out of the pump chamber, by which
amount the effective injection duration is lengthened. The speed of the
intermediate piston is correspondingly slower than that of the pump
piston. By the time a certain rpm during idling is attained, the effective
cross section of the throttle has become small enough that it no longer
affects the injection duration. This effect is attained quickly at
increasing rpm, so that a further blocking means in the relief conduit can
be dispensed with.
It is a further object of the invention that the throttle conduit can be
opened shortly before the end of the compression stroke, but still during
the intake stroke of the intermediate piston. Since the idling injection
quantities are small, and are injected at the late supply onset for
idling, and since the supply onset also depends on the filling ratio of
the pump chamber and with a high filling ratio there is usually an early
supply onset while with a low filling ratio there is usually a late supply
onset. Thus, lengthening of the injection duration is actually effective
only if a relatively small supply quantity is actually present, which is
injected at the desired late supply onset for idling, so that the
influence of this kind of lengthening of the injection duration no longer
exists during normal operation, even with earlier injected injection
quantities that are small but larger than the idling quantities.
It is still another object of the invention that the throttle conduit is
controlled by the intermediate piston. This provides an additional
influence on the injection duration lengthening, because the intermediate
piston does not interrupt the injection by uncovering a diversion conduit
until toward the end of its complete stroke, so that the opening up of the
throttle conduit containing the throttle does not take place until within
the stroke range of the intermediate piston that is already effective at
the remaining stroke corresponding to the idling quantity. With larger
injection quantities and a correspondingly longer effective stroke of the
intermediate piston serving the purpose of injection, fuel will thus flow
out through the throttle conduit only during this remaining stroke, and in
that conduit the effect of a lengthened injection duration is lessened or
becomes negligibly small.
In yet a further object of the invention, the pump chamber is relieved
toward a chamber of lower pressure, by means of the injection piston,
toward the end of the compression stroke. As a result, a uniform initial
situation for the particular filling of the pump chamber is attained for
each further cycle.
In still another object of the invention, the end of supply of injection is
effected by the opening up of a diversion conduit of the pressure chamber
toward the end of the pump piston compression stroke. This provides a
clear break with respect to the end of supply, and the effective injection
segment including the injection onset and end of injection, with respect
to the rotational angle of the crankshaft, or in a unit fuel injector with
respect to the rotational angle of the drive cam, depends on the
particular filling ratio of the pump chamber.
In yet another object of the invention, for diverting the pump chamber an
annular groove is present in the jacket face of the intermediate piston,
and this groove cooperates with an opening, present in the cylindrical
bore of the pump chamber, of a relief conduit leading to the chamber of
lower pressure; this opening is located upstream in the compression stroke
direction of an opening of the throttle conduit. This annular groove
provides a clean distinction between throttled outflow and diversion at
the end of the compression stroke.
In still a further object of the invention, the opening of the throttle
conduit is embodied as a throttle slit extending in the compression stroke
direction. This advantageously assures that the throttle cross section in
the remaining stroke range will increase with increasing stroke; that is,
the cross section of time during this stroke time that is effective for
lengthening the injection duration increases.
The invention will be better understood and further objects and advantages
thereof will become more apparent from the ensuing detailed description of
a preferred embodiment taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an injection system with a unit fuel injector in longitudinal
section, in highly simplified form;
FIG. 2 shows a detail of the unit fuel injector of FIG. 1 in a view showing
its structure; and
FIG. 3 is a function diagram with curves applying to the pump piston and
the intermediate piston one above the other.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the injection system having a unit fuel injector as shown in FIG. 1, a
pump piston 1 operates in a cylindrical bore 2 of a pump housing 3 and
defines a pump chamber 4, which is defined on its other end by an
intermediate piston 5 that is likewise axially movably disposed in the
cylindrical bore 2. A pressure chamber 6 is provided underneath the
intermediate piston 5, communicating via a pressure conduit 7 extending in
the housing 3 with a nozzle pressure chamber 8. The injection openings 9
of the unit fuel injector, which lead to a combustion chamber, not shown,
are controlled via a valve needle 11 that is loaded by a closing spring
12.
The pump piston 1 is driven for its reciprocating pumping motion by a drive
cam 13, rotating in the direction of the arrow I, counter to the force of
a restoring spring 14; the reciprocating pumping motion is indicated by a
double arrow II.
In this highly simplified illustration, no leakage conduits or
arrangements, which are present between the high-pressure part embodied by
the unit fuel injector and the low-pressure part to be explained below,
and which are necessary for function, are not shown. Associated with this
unit fuel injector is a low-pressure fuel system, not shown in further
detail here but belonging to the injection system, having a feed pump and
fuel metering devices, in particular in the form of magnet valves; these
elements are known per se and are not directly pertinent to the invention.
The intermediate piston 5 basically divides the pump chamber 4 from the
pressure chamber 6; these two work chambers are supplied with fuel
independently of one another. Via a supply onset control device 15, here
shown only symbolically as a block and normally including a feed pump and
a magnet valve, fuel is metered into the pump chamber 4 from a fuel
container 16 via a metering line 17.
There is a corresponding metering device 18 for the pressure chamber 6;
this metering device 18 likewise aspirates fuel from the fuel container 16
and pumps it into the pressure chamber 6 via a metering conduit 19. This
low-pressure fuel metering into the two work chambers 4 and 6 takes place
during the intake stroke of the pump piston 1 or intermediate piston 5.
Branching off from the cylindrical bore 2 are a relief conduit 21 and a
diversion conduit 22, which are each opened up by the intermediate piston
5 near its bottom dead center position, so that after that the pump
chamber 4 and the pressure chamber 6 are pressure-relieved to the fuel
container 16, by means of the relief conduit 21 and the diversion conduit
22, respectively.
Also branching off from the cylindrical bore 2 is a throttle conduit 23
including a throttle 42; this conduit 23 also discharges into the fuel
container 16 and is opened up by the intermediate piston 5 during the
compression stroke, shortly before the relief conduit 21 or diversion
conduit 22.
The supply onset control device 15 and the metering device 18 are triggered
by an electronic control unit 24, in order to determine the quantity of
fuel to be metered into the pump chamber 4 and pressure chamber 6 and
thereby regulate the supply onset or engine rpm. This electronic control
unit 24 is supplied with the load via a gas pedal 25 and with the rpm n
via an rpm transducer 26, as well as with the temperature T and a further
signal S, for instance an exhaust gas figure or an ambient air pressure
figure, via two other transducers, not shown. From the outputs 27 of this
electronic control unit 24, one output leads as shown via an electrical
line 28 to the supply onset control device 15 or to the metering device
18, while the other three outputs 27, in the case of a four-cylinder
engine, each lead to one other unit fuel injector having a supply onset
control device and a metering device. Naturally, the same feed pump
supplies fuel to both the supply onset control device 15 and the metering
device 18 of every unit fuel injector.
The intermediate piston 5 is urged in the direction of the pump chamber 4
by a control spring 29. There is an axial blind bore 31, open toward the
pressure chamber 6, in the intermediate piston which communicates through
a transverse bore 32 with an annular groove 33 disposed on the jacket face
of the intermediate piston 5. An axial blind bore 34 open toward the pump
chamber 4 is also present in the intermediate piston 5, communicating
through a transverse bore 35 with a second annular groove 36 disposed on
the jacket face of the intermediate piston 5. Toward the end of the
compression stroke of the intermediate piston 5, the annular groove 33
opens the diversion conduit 22, which directly interrupts the injection.
The annular groove 36, contrarily, after a certain compression stroke of
the intermediate piston 5 has been executed, opens the throttle conduit 23
so that fuel can flow out of the pump chamber 4 in a throttled manner; to
terminate the compression stroke of the intermediate piston 5 but also to
terminate the compression phase entirely, the groove 36 also opens the
relief conduit 21 upon the end of the compression stroke of the pump
piston 1.
The metering line 17 and the metering conduit 19 can have a flow through
them only in the direction toward the pump chamber 4 and pressure chamber
6, respectively, as indicated by the arrow. This can be achieved by the
inclusion of a check valve in the metering line 17. While in the case of
the metering conduit 19 fuel can always flow only in this metering
direction, for the metering line 17 it is also conceivable for it to have
a flow in the opposite direction, in other words toward the supply onset
control device 15, depending on whether the metering takes place into the
pump chamber 4, by means of a suitably limitedly metered fuel quantity, or
whether this chamber is completely filled and upon the compression stroke
some of this quantity, pumped into the pump chamber during the intake
stroke, can flow back out again, namely until such time as the intended
supply onset.
Between the pressure chamber 6 and the pressure conduit 7, there is a
pressure valve 37, to prevent a reverse flow from the nozzle pressure
chamber 8 to the pressure chamber 6, particularly during the intake
stroke.
The course of the contour of the drive cam 13 is divided into three parts,
namely an intake stroke part III for a relatively long intake stroke
segment; a base circle IV of the cam 13 for a short resting segment; and a
compression stroke part V for a steep compression stroke segment. In the
working position shown in FIG. 2, the drive cam 13 is just acting upon the
pump piston 1 with its base circle IV, just before the compression stroke
part V comes into play; as the drive cam 13 continues to rotate, the pump
piston is just beginning its downward compression stroke. The pump piston
1 accordingly assumes its top dead center position, which is equivalent to
a terminal position after the intake stroke and an initial position before
the compression stroke.
In this exemplary embodiment shown, the control spring 29 is supported at
one end on a collar 38 of the intermediate piston 5 and on the other on a
shoulder 39 of the cylindrical bore 2. The initial position of the
intermediate piston 5 shown in FIG. 1 is determined by a shoulder 41 of
the cylindrical bore 2.
FIG. 2 is a structural view of the middle region of the unit fuel injector,
namely the control region of the intermediate piston 5; the throttle 42 in
the throttle conduit 23 is embodied as a slitlike opening of the throttle
conduit 23 facing toward the cylindrical bore 2. This slitlike throttle 42
cooperates with the lower control edge 43 of the annular groove 36, and
FIG. 2 shows the moment at which this lower control edge 43 just begins to
open the throttle 42. After the execution of the stroke A, the relief
conduit 21 is then opened by this lower control edge 43. The diversion
conduit 22, contrarily, is opened up by the lower control edge 44 of the
annular groove 33 as soon as the stroke B is executed, so that for the
lengthening of the injection duration only this stroke B is effectively
operative; that is, there is a relatively shorter stroke than the stroke
for opening the throttle 42. At lower rpm, when the cross section of the
throttle 42 has a correspondingly major influence given the large time
cross section then present, the speed of the intermediate piston 5 is
braked severely, because some of the driving fluid is flowing out via the
throttle, so that the desired time that is intended to produce the
lengthening of the injection duration elapses for the execution of the
remaining stroke B; after that, i.e., after the opening of the diversion
conduit 22, the injection is suddenly interrupted. Nevertheless, the
intermediate piston 5 is displaced into its terminal position in a
correspondingly retarded manner, and in that position the pump chamber 4
is also relieved via the annular groove 36 toward the relief conduit 21.
The function of this fuel injection system will now be described, referring
to the diagram of FIG. 3. In this diagram, the stroke h of the pump piston
1 in the bottom of the diagram and the stroke z of the intermediate piston
5 in the top of the diagram are plotted on the ordinate, over the
rotational angle .alpha. of the camshaft 13 on the abscissa. The lower
curve describes the travel of the pump piston 1, while the upper curve
describes the travel of the intermediate piston 5.
If the pump piston 1 is driven out of its top dead center position shown in
FIG. 1, that is, its terminal intake stroke position, by rotating the
drive cam 13 in the direction of the arrow I, then the compression stroke
part V comes into action, and the pump piston 1 is displaced downward in
accelerated fashion in the direction of the arrow II. The total
compression stroke part V is equivalent in FIG. 3 to a rotational angle
.alpha.V, calculated from the origin. During a first compression stroke
segment h.sub.S of the pump piston 1, gas-filled voids present in the pump
chamber 4 are compensated for, so that after the rotational angle .alpha.S
there is only fluid in the pump chamber 4, and so a high pressure can
thereby be developed. The size of the void is determined during the intake
stroke by the supply onset control device 15, which meters only a
particular fuel quantity into the pump chamber 4. The greater this fuel
quantity, the smaller the remaining void to be compensated for during the
first compression stroke segment, and the shorter the compensation stroke
h.sub.S. However, the shorter the compensation stroke h.sub.S, the sooner
after the buildup of a pressure in the pump chamber 4 will the
intermediate piston 5 be driven for its own compression stroke.
The compression stroke of the intermediate piston 5 is effected counter to
the force of the control spring 29 and in a first segment namely up to
rotational angle .alpha.E (FIG. 3), it compensates for a void located in
the pressure chamber 6 until here again, because only fuel is still
present, a corresponding injection pressure can be established. This
injection pressure is determined above all by the injection nozzle, or in
other words by the throttling action of the injection openings 9, and by
the opening pressure determined by the closing spring 12 and by the cross
section of the valve needle 11 acted upon in the opening direction. At
that time, the pump piston 1 has executed the stroke h.sub.E, while the
intermediate piston 5 has executed the correspondingly shorter stroke
z.sub.E. The effectiveness of the stroke h.sub.S of the pump piston 1 is
accordingly dependent on the filling ratio of the pump chamber 4, and the
stroke z.sub.E of the intermediate piston 5 until injection can occur at
all, which stroke is only enabled thereafter, depends on the filling ratio
of the pressure chamber 6. The sum of these two prestrokes h.sub.S and
z.sub.E is the stroke h.sub.E of the pump piston 1 and determines the
onset of supply of fuel to the engine, or in other words the injection
onset. The actual onset of injection is thus determined not only by the
filling ratio of the pump chamber 4 but always by the addition of the
filling ratios of both work chambers 4 and 6. This relationship is taken
into account via the electronic control unit 24 by way of an injection
program; that is, with an increasing injection quantity or in other words
for a higher filling ratio in the pressure chamber 6, a corresponding
decrease in the filling ratio in the pump chamber 4 is effected for the
same supply onset. The extreme cases are a very early supply onset at
maximum injection quantity as is the case with full load, and a late
supply onset at very low rpm, as is the case during idling. At full load,
the stroke h.sub.S is accordingly very short, and so is the stroke z.sub.E
of the intermediate piston 5, so that work chambers 4 and 6 are filled to
an extremely full extent, while contrarily at idling the pump piston 1 and
the intermediate piston 5 have executed an extremely long stroke before a
high pressure required for the injection has become established in the
pressure chamber 6.
In FIG. 2, the intermediate piston 5 is shown in the stroke position
identified by z.sub.L in FIG. 3, at which time the lower control edge 43
of the annular groove 36 has just opened the throttle 42 of the throttle
conduit 23. Since the annular groove 36 communicates with the pump chamber
4 via the transverse bore 35 and the axial blind bore 34, a throttle
outflow from the pump chamber 4 exists from this instant and has a time
cross section, such time factor being dependent on the engine rpm and the
rpm of the camshaft 13. At this point the time cross section factor
depends only on the further stroke of the intermediate piston 5 and on the
then additionally exposed slit of the throttle 42. This effective throttle
slit enlarges in proportion to the stroke of the intermediate piston 5 and
can thus be programmed as a constant factor. The stroke of the
intermediate piston 5 is ended at z.sub.A, when the lower control edge 43
of the annular groove 36 opens the relief conduit 21, and the pump piston
1 driven onward to rotational angle .alpha.V pumps the fuel out of the
pump chamber 4 directly to the relief conduit 21. In each case, however,
the fuel stored before the intermediate piston 5 in the pressure chamber 6
for injection and metered during the intake stroke is injected via the
pressure valve 37, the pressure conduit 7, the nozzle pressure chamber 8
and the injection openings 9 into the engine, until the lower control edge
44 of the annular groove 33 in FIG. 2, after the execution of the stroke
B, opens the diversion conduit 22, thereby ending the injection. This is
attained after the intermediate piston 5 has covered the stroke z.sub.A.
Two different curve course for the same injection quantity are plotted in
the upper part of FIG. 3. The solid curves represents higher rpm, at a
small injection quantity corresponding to idling, as can occur for
instance during overrunning (traveling downhill without depressing the gas
pedal), so that the time cross section of the throttle conduit 23, or of
the throttle 42, is extremely short and thus has hardly any effect on a
lengthening of the injection duration. The upper curve is therefore in a
straight solid line, even through in fact, if it were shown exactly, there
would be a slight break (which is variable depending on the rpm) in the
curve from the point .alpha..sub.L on. Contrarily, the characteristic
curve c shown in dashed lines indicates the case in which the rpm is so
low, as in idling, that the time cross section of the slitlike throttle 42
is relatively large, and correspondingly more fuel flows out via this
throttle from the pump chamber 4 before the diversion conduit 22 is opened
by the annular groove 33. While in the first case the injection duration
has ended at a rotational angle .alpha..sub.A, it is lengthened in the
second case until rotational angle .alpha..sub.AL. This type of control
has a certain self-regulating effect because this "automatic" lengthening
of the injection duration becomes effective for fuel combustion only when
not only are the injection quantities relatively small but also the rpm is
relatively low (idling).
Upon further rotation of the drive cam 13 in the direction of the arrow I,
the relatively long intake stroke part III comes into action, during which
the pump piston 1 and the intermediate piston 5, driven by the restoring
spring 14 of the pump piston 1 and the control spring 29 of the
intermediate piston 5, return to the initial position shown in FIG. 1.
This is attained at a rotational angle .alpha.III until after the travel
of the base circle IV, that is, at rotational angle .alpha.IV, a new
compression stroke begins. During the intake stroke, once the annular
groove 33 is disconnected from the diversion conduit 22, from rotational
angle .alpha.Z, a fuel quantity to be injected in the next injection cycle
is metered into the pressure chamber 6 via the metering device 18 and the
metering conduit 19. The maximum possible quantity is determined by the
possible stroke of the intermediate piston 5, which is defined by the
shoulder 41. The intermediate piston 5 strikes this shoulder 41 at the
rotational angle .alpha.K, whereupon in the compression chamber 6, once
the metering is ended, a void is created because the control spring 29
displaces the intermediate piston 5 completely against the shoulder 41. No
later than after that, the metering of the fuel into the pump chamber 4 by
the supply onset control device 15 takes place, to define the onset of
supply, and in combination with the injection quantity, to define the end
of supply. In each case, however, this metering into the pump chamber 4
does not take place under after the instant when the annular groove 36 is
again disconnected from the throttle conduit 23, namely from rotational
angle .alpha.D on.
The foregoing relates to a preferred exemplary embodiment of the invention,
it being understood that other variants and embodiments thereof are
possible within the spirit and scope of the invention, the latter being
defined by the appended claims.
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